This disclosure relates to a vapor delivery device, methods of manufacture and methods of use thereof. In particular, this disclosure relates to a high output, high capacity delivery device for delivering liquid precursor compounds in the vapor phase to reactors.
Semiconductors comprising Group III-V compounds are used in the production of many electronic and optoelectronic devices such as lasers, light emitting diodes (LEDS), photodetectors, and the like. These materials are used for manufacturing different monocrystalline layers with varying compositions and with thicknesses ranging from fractions of a micrometer to a few micrometers. Chemical vapor deposition (CVD) methods using organometallic compounds are generally employed for the deposition of metal thin-films or semiconductor thin-films, such as films of Group III-V compounds. Such organometallic compounds may be either liquid or solid.
In CVD methods, a reactive gas stream is generally delivered to a reactor to deposit the desired film for electronic and optoelectronic devices. The reactive gas stream is composed of a carrier gas, such as hydrogen, entrained with vapors of a precursor compound. When the precursor compound is a liquid (hereinafter liquid precursor compound), a reactive gas stream is generally obtained by passing (i.e., bubbling) a carrier gas through the liquid precursor compound in a delivery device (i.e., a bubbler). The delivery device comprises a bath surrounding a container that holds the liquid precursor compound.
Liquid precursor compounds have a specific enthalpy of vaporization of 2.0 to 10.0 watt-minute per gram. When there is no carrier gas flow through the delivery device the temperature difference between the bath and the liquid precursor compound is zero and no energy is expended in the delivery device. On the other hand, when it is desired to deliver the liquid precursor compound to the reactor at a particular temperature, the carrier gas is permitted to flow through the liquid precursor compound as a result of which the liquid precursor compound cools down. This cooling is undesirable because temperature variations in the liquid precursor compound lead to variable amounts of the liquid precursor compound being delivered to the reactor. The bath, in order to compensate for the temperature variations, now transfers energy to the delivery device in the form of heat in order to attempt to maintain the liquid precursor compound at a constant temperature. The temperature difference between the bath and the liquid precursor compound is therefore no longer zero. Since heat is supplied from the bath to the liquid precursor compound, the temperature of the liquid precursor compound is now not accurately known (i.e., there are temperature variations in the liquid precursor compound).
Early liquid precursor compound delivery devices were long, narrow cylinders, i.e. aspect ratio of greater than 2, which were capable of holding a volume equivalent to 200 grams of a particular liquid precursor compound. The delivery device therefore had a large surface area to liquid precursor compound mass ratio and could easily be fully immersed in commercially available constant-temperature baths. The carrier gas flows were small and thus temperature differences between the bath and the liquid precursor compound were negligible. The liquid precursor compound flux in moles per minute was known within 1 weight percent (wt %) with little change throughout the use of the bubbler.
Current liquid precursor compound delivery devices are larger than the early liquid precursor compound delivery devices and use lower-aspect-ratio cylinders (that have height-to-diameter aspect ratios of less than 2) as compared with the earlier devices. Current delivery devices contain more than 2 kilograms of liquid precursor compound, and may contain up to 10 kilograms of liquid precursor compound. These large cylinders do not normally fit into commercially available constant-temperature baths. Portions of the cylinder top often are exposed to the ambient air and thus become an unintentional source of heat or cooling to the liquid precursor compound depending upon ambient conditions.
In addition, carrier gas flows of around 1 standard liter per minute and vaporization rates of 1 gram per minute of liquid precursor compound are used in these larger current liquid precursor compound delivery devices, thus using 5 watts of energy for the vaporization. As a result, the liquid precursor compound temperature easily deviates more than 2° C. from the bath temperature, which can result in a deviation in the liquid precursor compound flux of up to 10 wt %.
Another concern with the larger current liquid precursor compound delivery devices is the time it takes to reach a steady state of precursor compound flux. The chemical process in the reactor cannot proceed until the flux of liquid precursor compound vapors from the delivery device is stabilized. The time to stabilize the liquid precursor compound flux depends mainly on heat transfer area and the mass of the liquid precursor compound in the delivery device. Both of these parameters are only approximately known. Upon starting the carrier gas flow, the liquid precursor compound uses its internal heat for evaporation, thus resulting in a cooling down of the liquid precursor compound. A relatively large liquid precursor compound mass results in a relatively longer time period to reach a steady state temperature, whereas a relatively smaller liquid precursor mass results in a relatively shorter time period to reach a steady state temperature. The time it takes to reach a steady state temperature depends on the heat transfer area and on the remaining mass.
There therefore remains a need for improved delivery devices and methods for delivering vapors of a liquid precursor compound from a large delivery device, where at least 1 watts of energy is utilized for the vaporization. It is also desirable to have a delivery device that can deliver a uniform and high flux of the precursor vapor throughout the process up to depletion of the liquid precursor compound from the delivery device, while using carrier gas flows that are greater than 1 standard liter per minute.
A delivery system for a liquid precursor compound comprises a delivery device having an inlet port and an outlet port; a first proportional valve; wherein the delivery device is in operative communication with a first proportional valve; wherein the first proportional valve is operative to control the flow of the carrier gas based on an applied voltage; a physical-chemical sensor; the physical-chemical sensor being disposed downstream of the delivery device and being operative to analyze chemical contents of a fluid stream emanating from the delivery device; the physical-chemical sensor being in communication with the first proportional valve; and a first pressure/flow controller being in operative communication with the physical-chemical sensor and with the first proportional valve; wherein the delivery system is operative to deliver a substantially constant number of moles per unit of time of a liquid precursor compound vapor to each of a plurality of reactors that are in communication with the delivery system; where the liquid precursor compound is in a liquid state in the delivery device.
A method comprises transporting a first stream of a carrier gas to a delivery device; the delivery device containing a liquid precursor compound; the first stream of carrier gas being at a temperature greater than or equal to 20° C.; transporting a second stream of the carrier gas to a point downstream of the delivery device; wherein a flow direction of the first stream and a flow direction of the second stream are not opposed to each other; and combining the first stream after it emanates from the delivery device and the second stream to form a third stream; where a dew point of a vapor of the precursor compound in the third stream is lower than an ambient temperature.